<template>
  <div>
    <p>app</p>
    <button @click="count++">{{ count }}</button>
    <Child :num="count"></Child>
  </div>
</template>

<script>
import Child from './Child'
export default {
  components: {
    Child
  },
  data () {
    return {
      count: 100
    }
  }
}
</script>

<style>
  p {
    color: red
  }
</style>